<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>demo</title>
  <script src="https://cdn.jsdelivr.net/npm/vue"></script>
</head>
<body>
<div id="app">
  <p>{{message}}</p>
</div>

<script>

  var app = new Vue({
      el: '#app',
      data: {
          message: "This is a demo written by lazy"
      },
      mounted: function () {
          alert("mounted")
      }
  })

</script>

</body>
</html>